Three types of disk drives, namely a solid state drive (SSD), a serial attached small computer system interface (SCSI) (SAS) disk, and a serial advanced technology attachment (SATA) disk, can be listed as examples of disk drives to be used in storage systems such as a disk array system. As illustrated in FIG. 1, in terms of reliability and performance, among the three types of disk drives, an SSD comes first, an SAS disk comes second, and an SATA disk comes third.
If a server employs a storage device that includes a hierarchized disk (see FIG. 1) having the three types of disks that differ in characteristics as mentioned above, storage hierarchization control as described below is carried out. Specifically, with a configuration that employs a hierarchized disk, a data block to be relocated and a disk to which that data block is to be relocated are determined on the basis of the frequency of access at a disk side, and the data block is relocated accordingly, as illustrated in FIG. 1.
For example, if the frequency of access to a given data block, included in a file on the SSD is low, that data block is moved from the SSD to the SAS disk and is relocated on the SAS disk. Similarly, if the frequency of access to a given data block on the SAS disk is low, that data block is moved from the SAS disk to the SATA disk and is relocated on the SATA disk. Meanwhile, if the frequency of access to a given data block on the SATA disk increases, that data block is moved from the SATA disk to the SAS disk and is relocated on the SAS disk. Similarly, if the frequency of access to a given data block on the SAS disk increases, that data block is moved from the SAS disk to the SSD and is relocated on the SSD.
Japanese Laid-open Patent Publication No. 2006-4011 is an example of related art.